Currently, with respect to mobile communications that employ an OFDMA (Orthogonal Frequency Division Multiple Access) scheme, when performing communications by way of beamforming, a reference signal specific to each base station device (e.g., a common reference signal (CRS)), a reference signal specific to each mobile station device (e.g., a dedicated reference signal (DRS)), and a data signal are arranged in a resource block. Here, the reference signal specific to each base station device is used chiefly in the reproduction of a control signal, in measuring channel quality, and so forth. The reference signal specific to each mobile station device is used chiefly in the reproduction of the data signal. It is noted that since the reproduction of a control signal, measuring channel quality, etc., are not the characterizing parts of the present invention, descriptions pertaining to the control signal, and the measuring of channel quality will herein be omitted.
On the other hand, there is a problem in that, when the reference signal specific to each base station device and the reference signal specific to each mobile station device are mixed within one OFDM (Orthogonal Frequency Division Multiplexing) symbol of the resource block, restrictions for frequency shifting the reference signal specific to each base station device and the reference signal specific to each mobile station device become stringent.
In addition, under such conditions where the power of the reference signal specific to each base station device is uniform within the resource block, and where the power of the data signal within the OFDM symbol including the reference signal specific to each base station device is uniform within the resource block, when increasing the power of the reference signal specific to each base station device in order to improve cell coverage, cell edge throughput, etc., there is a problem in that, as shown in FIG. 1A, because the number of data signals in OFDM symbols in which the reference signal specific to each base station device and the reference signal specific to each mobile station device are mixed is less than the number of data signals within OFDM symbols including the reference signal specific to each base station device, the power of the data signals within OFDM symbols including only the reference signal specific to each base station device becomes unnecessarily low. For example, whereas the total power of the third OFDM symbol is 24a, the total power of the fourth OFDM is 20a as indicated with the arrow in FIG. 1A. As such, at the fourth OFDM symbol, the data signals drop by an extra 4a.
First, in Non-Patent Document 1, there is presented a problem wherein when a reference signal specific to each base station device and a reference signal specific to each mobile station device are mixed within one OFDM symbol of a resource block, restrictions for frequency shifting the reference signal specific to each base station device and the reference signal specific to each mobile station device become stringent.
In Non-Patent Document 1, in order to overcome this problem, as shown in FIG. 1B, it is proposed that the reference signal specific to each mobile station device in the eighth OFDM symbol be moved to the ninth OFDM symbol so that the reference signal specific to each base station device and the reference signal specific to each mobile station device would not be mixed within one OFDM symbol.
Next, in Non-Patent Document 2, the relationship between the power of a reference signal specific to each mobile station device and the power of a data signal is described.
In Non-Patent Document 2, the power of a reference signal specific to each mobile station device is defined as being the same as the power of a data signal within an OFDM symbol of the same resource block as that reference signal specific to each mobile station device and that does not include a reference signal specific to each base station device.
Next, in Non-Patent Document 3, there is proposed a method for increasing the power of a reference signal specific to each base station device in order to improve cell coverage, cell edge throughput, etc.
In Non-Patent Document 3, as shown in FIG. 2, an SFBC (Space Freqency Block Code)+FSTD (Frequency Switched Transmit Diversity) encoding process is considered. It is proposed that the power of a data signal within the same OFDM symbol as a reference signal specific to each base station device be decreased in order to increase the power of that reference signal specific to each base station device within one OFDM symbol of a resource block.
In Non-Patent Document 3, because the power of the data signal decreases, diversity gain decreases, and throughput characteristics, etc., degrade.
Next, in Non-Patent Document 4, the power of a reference signal specific to each base station device is increased in order to improve cell coverage, cell edge throughput, etc. Here, as shown in FIG. 3, SFBC (Space Freqency Block Code)+FSTD (Frequency Switched Transmit Diversity) encoding is considered. It is proposed that unused subcarriers be set within the same OFDM symbol as a reference signal specific to each base station device in order to increase the power of that reference signal specific to each base station device within one OFDM symbol of a resource block.
In Non-Patent Document 4, because the power of the data signal does not decrease, there is no degradation in throughput characteristics, etc., that results therefrom. However, there are concerns that throughput characteristics, etc., may degrade by an amount corresponding to data signals that may be arranged in the unused subcarriers.
Next, in Non-Patent Document 5, as shown in FIG. 4, it is demonstrated that when performing communications by way of beamforming, the accuracy of channel estimation is improved by increasing the power (for example, from 2 a to 5 a) of a reference signal specific to each mobile station device. In conjunction therewith, the power of a data signal within an OFDM symbol of the same resource block as the reference signal specific to each mobile station device, whose power is increased, is decreased.
In Non-Patent Document 5, such results as those shown in FIG. 5 are demonstrated. FIG. 5 is a diagram where a case in which the modulation scheme is 64 QAM (Quadrature Amplitude Modulation) and a case in which the modulation scheme is QPSK (Quadrature Phase Shift Keying) are compared, thereby demonstrating the influence the magnitude of the power of the reference signal specific to each mobile station device has on throughput characteristics.
As shown in FIG. 5, it can be seen that the best throughput is achieved when the power of the reference signal specific to each mobile station device is increased by 0.5 [dB]. The reason for this is speculated to be that beamforming gain decreases when the power of the data signal is decreased.
Accordingly, for a case in which communications are performed by way of beamforming, attempts to improve throughput were limited to an increase by 0.5 [dB] or so at most for the power of the reference signal specific to each mobile station device.
Non-Patent Document 1: 3GPP TSG RAN1 #47bis, R1-082508, “Modification on UE-Specific RS for Extended CP”
Non-Patent Document 2: 3GPP TSG RAN1 #52bis, R1-082607, “Way forward on DRS EPRE”
Non-Patent Document 3: 3GPP TSG RAN1 #46bis, R1-062608, “Issues of non-overlapping DL reference signal with power boosting”
Non-Patent Document 4: 3GPP TSG RAN1 #47bis, R1-070250, “Downlink transmit power boosting”
Non-Patent Document 5: 3GPP TSG RAN1 #53, R1-081779, “DRS Power Boosting”